Plasma processing apparatus and plasma processing method

ABSTRACT

In a plasma processing apparatus, a first electrode is attached to a grounded evacuable processing chamber via an insulating material or a space and a second electrode disposed in parallel with the first electrode spaced apart therefrom in the processing chamber, the second electrode supporting a target substrate to face the first electrode. A first radio frequency power supply unit applies a first radio frequency power of a first frequency to the second electrode, and a second radio frequency power supply unit applies a second radio frequency power of a second frequency lower than the first frequency to the second electrode. Further, a processing gas supply unit supplies a processing gas to a processing space formed by the first and the second electrode and a sidewall of the processing chamber. Moreover, an inductor electrically is connected between the first electrode and a ground potential.

FIELD OF THE INVENTION

The present invention relates to a technique for performing a plasmaprocessing on a target substrate; and, more particularly, to acapacitively coupled plasma processing apparatus of a dual frequencyapplication mode and a plasma processing method.

BACKGROUND OF THE INVENTION

In a manufacturing process of semiconductor devices or flat paneldisplays (FPDs), a plasma is used to perform a processing, such asetching, deposition, oxidation, sputtering or the like, so as to obtaina good reaction of a processing gas at a relatively low temperature.Conventionally, a capacitively coupled type plasma apparatus has beenwidely employed as a single-wafer plasma processing apparatus,especially, as a single-wafer plasma etching apparatus.

Generally, in the capacitively coupled plasma processing apparatus, anupper electrode and a lower electrode are disposed to face each other inparallel in a vacuum processing chamber, a substrate to be processed (asemiconductor wafer, a glass substrate or the like) is mounted on theupper electrode, and a radio frequency voltage is applied to either oneof the upper and the lower electrode. Electrons are accelerated by anelectric field formed by the radio frequency voltage to collide with aprocessing gas. As a result of ionization by the collision between theelectrons and the processing gas, a plasma is generated, and a desiredmicroprocessing (for example, etching) is performed on the surface ofthe substrate by radicals or ions in the plasma. At this time, theelectrode to which the radio frequency voltage is applied is connectedwith a radio frequency power supply via a blocking capacitor in amatching unit and thus serves as a cathode. A cathode coupling method inwhich the radio frequency voltage is applied to the lower electrode,serving as the cathode, for supporting the substrate enables ananisotropic etching by substantially vertically attracting ions in theplasma to the substrate with a self-bias voltage generated in the lowerelectrode.

In the capacitively coupled plasma processing apparatus of the dualfrequency application type, a first radio frequency power of arelatively radio frequency (generally, 27 MHz or greater) for plasmageneration and a second radio frequency power of a relatively lowfrequency (generally, 13.56 MHz or less) for ion attraction are appliedto the lower electrode (see, e.g., Japanese Patent Laid-open PublicationNo. 2000-156370 and U.S. Pat. No. 6,642,149).

The dual frequency application is advantageous in that plasma densityand anisotropic etching selectivity can be individually optimized by thefirst and the second radio frequency power, and also in that the secondradio frequency power of a relatively low frequency can effectivelyprevent or suppress a deposit adhesion during a process in whichdeposits such as polymer and the like are adhered to an upper electrode.Specifically, when the ions are incident on the upper electrode servingas an anode, a deposited film (and an oxide film, if it exists) adheredto the electrode is sputtered by ion impact. The number of ions used forthe sputtering is determined by the first radio frequency. Further, anelectric field that accelerates the ions is generated by the secondradio frequency power of the relatively low frequency.

In the conventional capacitively coupled plasma processing apparatus ofthe dual frequency application type as described above, the upperelectrode serving as the anode to which no radio frequency is applied isDC-grounded generally. Typically, a processing chamber, which is framegrounded, is formed of metal, e.g., aluminum, a stainless steel or thelike, so that the upper electrode can be held at ground potential viathe processing chamber. Accordingly, the upper electrode is directlyattached to a ceiling of the processing chamber to be integrallyassembled thereto or the ceiling of the processing chamber itself isused as the upper electrode.

With a recent trend of miniaturization of design rules for themanufacturing process, a high-density plasma is required to be availableat a low pressure for a plasma processing. In the capacitively coupledplasma processing apparatus in which dual frequency powers are appliedto the lower electrode, the frequency of the first radio frequencypower, which mainly contributes to a plasma generation, tends to begradually increased and a frequency of 40 MHz or greater is standardlyused in recent years. However, if the frequency of the radio frequencypower becomes high, a radio frequency current is made to be concentratedon a central portion of the electrode, so that a density of a plasmagenerated in a processing space between two electrodes becomes higher atthe central portion of the electrode than that at the edge portionthereof. As a result, there occurs a problem that processcharacteristics become nonuniform in a radial direction. Meanwhile,since the frequency of the second frequency power that mainlycontributes to ion attraction is relatively low, it is not focused onthe central portion of the electrode. In other words, in theconventional apparatus in which the upper electrode is directly attachedto or formed integral with the processing chamber to be DC-groundedtherethrough, the functions of the second radio frequency power thatinclude attracting the ions toward the substrate and suppressing thedeposit adhesion to the upper electrode are not deteriorated.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide acapacitively coupled plasma processing apparatus and method of a dualfrequency application type in which two kinds of radio frequency powersare applied to an electrode for supporting a target substrate thereon,wherein in-surface uniformity of processes can be improved bycontrolling plasma density spatial distribution characteristics whilepreventing or suppressing an undesired film from being formed on anotherelectrode facing the electrode for supporting the target substrate.

In accordance with a first aspect of the invention, there is provided aplasma processing apparatus including: an evacuable processing chamberwhich is grounded; a first electrode attached to the processing chambervia an insulating material or a space; a second electrode disposed inparallel with the first electrode spaced apart therefrom in theprocessing chamber, the second electrode supporting a target substrateto face the first electrode; a first radio frequency power supply unitfor applying a first radio frequency power of a first frequency to thesecond electrode; a second radio frequency power supply unit forapplying a second radio frequency power of a second frequency lower thanthe first frequency to the second electrode; a processing gas supplyunit for supplying a processing gas to a processing space formed by thefirst and the second electrode and a sidewall of the processing chamber;and an inductor electrically connected between the first electrode and aground potential.

In accordance with a second aspect of the invention, there is provided aplasma processing method including the steps of: disposing a first and asecond electrode in parallel with a gap present therebetween in anevacuable processing chamber which is grounded; connecting the firstelectrode with a ground potential via a capacitive member and aninductive member, both being electrically arranged in parallel;supporting a target substrate on the second electrode to face the firstelectrode; vacuum exhausting an inside of the processing chamber to aspecific pressure level; and supplying a processing gas into aprocessing space defined by the first and the second electrode and asidewall of the processing chamber while applying to the secondelectrode a first radio frequency power of a first frequency and asecond radio frequency power of a second frequency lower than the firstfrequency, thereby generating a plasma from the processing gas in theprocessing space and performing a specified process on the targetsubstrate by using the plasma, wherein in frequency-impedancecharacteristics of a radio frequency transmission line from a boundarysurface between the processing space and the first electrode to theground potential via the first electrode, the frequency-impedancecharacteristics are set to make an impedance corresponding to the secondfrequency lower than that corresponding to the first frequency.

In the capacitively coupled plasma etching apparatus and method inaccordance with the first and second aspects of the present invention,when the first radio frequency power from the first radio frequencypower supply is applied to the second electrode, the plasma of theprocessing gas is generated in the processing space by a radio frequencydischarge between the first and the second electrode and that betweenthe second electrode and the sidewall (inner wall) of the processingchamber. Next, the plasma thus generated is diffused in all directions,especially in upward and outwardly radial directions, so that anelectron current in the plasma flows to the ground via the firstelectrode, the sidewall of the processing chamber and the like. When thesecond radio frequency power from the second radio frequency powersupply is applied to the second electrode, ions in the plasma whichvibrate according to the second radio frequency are attracted into thesubstrate due to a self-bias voltage generated in the second electrode.Also, the ions are incident on the first electrode to sputter a surfacethereof and removing a deposited film and the like therefrom, if theyexist.

In accordance with the first and second aspects of the presentinvention, the first electrode is attached to the processing chamber ata ground potential via an insulator or a space and is connected with theground potential via an inductive member or an inductor. Accordingly, anequivalent circuit in a radio frequency transmission line from aboundary surface between the processing space and the first electrode tothe ground potential via the first electrode becomes a parallel LCcircuit in which a coil component of an inductor is connected with acapacitive component of an insulator in parallel.

Generally, an impedance in the parallel LC circuit increases at aspecific frequency (antiresonacne frequency) while it considerablydecreases at a frequency away from the antiresonance frequency. Byutilizing those characteristics, in the plasma processing apparatus ofthe first aspect of the present invention, it is possible to provide ahigh impedance at the first radio frequency and a low impedance at thesecond radio frequency. In accordance with an embodiment of the presentinvention, the antiresonance frequency is obtained within a range fromabout 5 MHz to about 200 MHz in the frequency-impedance characteristicsin the above equivalent circuit or parallel LC circuit.

Due to the high impedance at the first radio frequency, the first radiofrequency current hardly flows from the second electrode to the firstelectrode. Accordingly, there is relatively increased a portion of anelectron current in the plasma flowing in the sidewall of the processingchamber, which makes the plasma density widen in the outwardly radialdirections. In this way, by optimally increasing the impedance at thefirst radio frequency in the parallel LC circuit, plasma density spatialdistribution characteristics can be controlled to be uniformdiametrically. Meanwhile, by decreasing the impedance at the secondradio frequency in the parallel LC circuit, the ions in the plasma whichvibrate according to the second radio frequency are incident onto thefirst electrode with a strong impact. As a result, an undesired filmadhered to a surface thereof can be effectively sputtered (removed)therefrom.

In accordance with a third aspect of the invention, there is provided aplasma processing apparatus including: an evacuable processing chamberwhich is grounded; a first electrode attached to the processing chambervia an insulating material or a space; a second electrode disposed inparallel with the first electrode spaced apart therefrom in theprocessing chamber, the second electrode supporting a target substrateto face the first electrode; a first radio frequency power supply unitfor applying a first radio frequency power of a first frequency to thesecond electrode; a second radio frequency power supply unit forapplying a second radio frequency power of a second frequency lower thanthe first frequency to the second electrode; a processing gas supplyunit for supplying a processing gas to a processing space formed by thefirst and the second electrode and a sidewall of the processing chamber;and an inductor and a capacitor electrically connected in series betweenthe first electrode and a ground potential.

In accordance with a fourth aspect of the invention, there is provided aplasma processing method including the steps of: disposing a first and asecond electrode in parallel with a gap present therebetween in a vacuumevacuable processing chamber which is grounded; connecting the firstelectrode with a ground potential via a capacitive member and aninductive member, both being electrically arranged in serial-paralleltherewith; supporting a target substrate on the second electrode to facethe first electrode; vacuum exhausting an inside of the processingchamber to a specific pressure level; supplying a processing gas into aprocessing space defined by the first and the second electrode and asidewall of the processing chamber while applying to the secondelectrode a first radio frequency power of a first frequency and asecond radio frequency power of a second frequency lower than the firstfrequency, thereby generating a plasma from the processing gas in theprocessing space and performing a specified process on the targetsubstrate by using the plasma, wherein in frequency-impedancecharacteristics of a radio frequency transmission line from a boundarysurface between the processing space and the first electrode to theground potential via the first electrode, the frequency-impedancecharacteristics are set to make an impedance corresponding to the secondfrequency lower than that corresponding to the first frequency.

In the third and the fourth aspect of the present invention, anequivalent circuit in a radio frequency transmission line from theboundary surface between the processing space and the first electrode tothe ground potential via the first electrode is configured as aserial-parallel LC circuit. In this serial-parallel LC circuit, animpedance extremely decreases at a specific frequency (resonancefrequency) and extremely increases at another specific frequency(antiresonance frequency). By utilizing those characteristics, a highimpedance and a low impedance can be obtained at the first and thesecond radio frequency, respectively. In accordance with an embodimentof the present invention, the resonance frequency is obtained within arange from about 0.1 kHz to about 15 MHz and the antiresonance frequencyis obtained within a range from about 5 MHz to about 200 MHz in thefrequency-impedance characteristics of the equivalent circuit or theserial-parallel LC circuit. By optimally increasing the impedance at thefirst radio frequency in the serial-parallel LC circuit, plasma densityspatial distribution characteristics can be controlled to be uniformdiametrically. Further, by decreasing the impedance at the second radiofrequency in the serial-parallel LC circuit substantially to a level atwhich a short-circuit occurs, the sputtering effect of removing anundesired film from the surface of the first electrode can be furtherenhanced.

In accordance with a fifth aspect of the invention, there is provided aplasma processing apparatus including: an evacuable processing chamberwhich is grounded; a first electrode attached to the processing chambervia an insulating material or a space; a second electrode disposed inparallel with the first electrode space apart therefrom in theprocessing chamber, the second electrode supporting a target substrateto face the first electrode; a first radio frequency power supply unitfor applying a first radio frequency power of a first frequency to thesecond electrode; a second radio frequency power supply unit forapplying a second radio frequency power of a second frequency lower thanthe first frequency to the second electrode; a processing gas supplyunit for supplying a processing gas to a processing space formed by thefirst and the second electrode and a sidewall of the processing chamber;a DC power supply for applying a DC voltage to the first electrode; anda filter electrically connected between the first electrode and the DCpower supply, the filter allowing a direct current to substantially passtherethrough while having desired frequency-impedance characteristicsfor a radio frequency.

In the plasma processing apparatus in accordance with the fifth aspectof the present invention, since a desired DC voltage is applied from theDC power supply to the first electrode via the filter to obtain actingeffects thereby. Further, the functions of the first and the secondradio frequency can be corrected, controlled or assisted by thefrequency-impedance characteristics of the filter. For example, when thefilter is provided in the serial-parallel LC circuit as in the secondplasma processing apparatus, it is possible to improve the plasmadensity spatial distribution characteristics or the sputtering effectfor the first electrode (which removes an undesired film therefrom).

In accordance with the plasma processing apparatus and the plasmaprocessing method of the present invention, it is possible to resolve atradeoff in the functions of the first and the second radio frequency inthe capacitively coupled apparatus of a dual frequency application type(wherein two radio frequency powers are applied to an electrode) withthe above-described configurations and operations. Especially, thein-surface uniformity of processes can be improved by controlling theplasma density spatial distribution characteristics while preventing orsuppressing an undesired film from being formed on the other electrodefacing the electrode to which two radio frequency powers are applied.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of embodiments, given inconjunction with the accompanying drawings, in which:

FIG. 1 is a vertical cross sectional view of a plasma etching apparatusin accordance with a first embodiment of the present invention;

FIG. 2 schematically shows a capacitively coupled radio frequencydischarge system in a plasma etching apparatus of a comparative example;

FIG. 3 schematically illustrates a capacitively coupled radio frequencydischarge system in the plasma etching apparatus shown in FIG. 1;

FIG. 4 describes an example of frequency-impedance characteristics in aradio frequency transmission line to a ground potential via an upperelectrode in the plasma etching apparatus shown in FIG. 1;

FIG. 5A depicts in-surface distribution characteristics of an etchingrate of an oxide film in a test example in accordance with the presentinvention;

FIG. 5B presents in-surface distribution characteristics of an etchingrate of a photoresist in the test example;

FIG. 6A represents in-surface distribution characteristics of an etchingrate of an oxide film in a first comparative example;

FIG. 6B describes in-surface distribution characteristics of an etchingrate of a photoresist in the first comparative example;

FIG. 7A offers in-surface distribution characteristics of an etchingrate of an oxide film in a second comparative example;

FIG. 7B provides in-surface distribution characteristics of an etchingrate of a photoresist in the second comparative example;

FIG. 8 illustrates a vertical cross sectional view of a plasma etchingapparatus in accordance with a second embodiment of the presentinvention;

FIG. 9 is a circuit diagram showing an exemplary configuration of acircuit in a DC filter unit of the plasma etching apparatus;

FIG. 10 depicts an example of frequency-impedance characteristics of aserial-parallel LC circuit in the DC filter unit and an example offrequency-impedance characteristics in a radio frequency transmissionline to a ground potential via an upper electrode in the plasma etchingapparatus shown in FIG. 2;

FIG. 11 shows a circuit diagram of a modified configuration of thecircuit in the DC filter unit;

FIG. 12 sets forth a circuit diagram of a modification of theserial-parallel LC circuit in the second embodiment of the presentinvention;

FIG. 13 describes a fragmentary cross sectional view of an example of acapacitance varying unit in the plasma etching apparatus in accordancewith the second embodiment of the present invention;

FIG. 14 offers a fragmentary cross sectional view of another example ofthe capacitance varying unit in the plasma etching apparatus inaccordance with the second embodiment of the present invention;

FIG. 15 presents a fragmentary cross sectional view of still anotherexample of the capacitance varying unit in the plasma etching apparatusin accordance with the second embodiment of the present invention; and

FIG. 16 represents a vertical cross sectional view of a plasma etchingapparatus in accordance with a modification of the second embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1 illustrates a configuration of a plasma processing apparatus inaccordance with a first embodiment of the present invention. The plasmaprocessing apparatus is configured as a capacitively coupled (parallelplate type) plasma processing apparatus of a type in which dualfrequency powers are applied to a lower electrode. The plasma processingapparatus has a cylindrical vacuum chamber (processing chamber) 10 madeof, e.g., an aluminum whose surface is alumite-treated (anodicallyoxidized), and the chamber 10 is frame grounded.

A cylindrical susceptor support 14 is provided at a bottom portion inthe chamber 10 via an insulation plate 12 made of ceramic or the like.Further, a susceptor 16 made of, e.g., aluminum, is disposed above thesusceptor support 14. The susceptor 16 serves as a lower electrode and atarget substrate, e.g., a semiconductor wafer W, is mounted thereon.

On the top surface of the susceptor 16, there is disposed anelectrostatic chuck 18 for attracting and holding the semiconductorwafer with an electrostatic adsorptive force. The electrostatic chuck 18includes an electrode 20 formed of a conductive film which is insertedbetween a pair of insulating layers or sheets. A DC power supply 22 isconnected to the electrode 20. The electrostatic chuck 18 is allowed toattract and hold the semiconductor wafer W thereon with a Coulomb forcegenerated by a DC voltage applied from the DC power supply 22 thereto. Afocus ring 24 made of, e.g., silicon is disposed to surround theelectrostatic chuck 18 to improve an etching uniformity. Further, aninner wall member 25 made of, e.g., quartz is attached to the sidesurfaces of the susceptor 16 and the susceptor support 14.

A coolant path 26 is circumferentially provided inside the susceptorsupport 14. A coolant, e.g., cooling water, of a specific temperature issupplied into and circulated along the coolant path 26 from an externalchiller unit (not shown) via coolant lines 27 a, 27 b. Accordingly, theprocessing temperature of the semiconductor wafer W on the susceptor 16can be controlled by the temperature of the coolant. Further, athermally conductive gas, e.g., He gas, is supplied into a gap betweenthe top surface of the electrostatic chuck and the backside of thesemiconductor wafer W from a thermally conductive gas supply unit (notshown) via a gas supply line 28.

The susceptor 16 is electrically connected with a first and a secondradio frequency power supply 30 and 70 via matching units 32 and 72 andpower feed rods 33 and 74, respectively. The first radio frequency powersupply 30 outputs a radio frequency power of a specific frequency, e.g.,40 MHz, for plasma generation. Meanwhile, the second radio frequencypower supply 70 outputs a radio frequency power of a specific frequency,e.g., 2 MHz, which mainly contributes to ion attraction toward thesemiconductor wafer W on the susceptor and to prevention of an adhesionof an undesired film such as a deposited film, an oxide film or the liketo an upper electrode 34 and removal of the undesired film which will bedescribed later.

The upper electrode 34 is provided above the susceptor 16 to face thesusceptor 16 in parallel. Further, the upper electrode 34 has anelectrode plate 36 having a plurality of gas injection openings 36 a andan electrode support 38 for detachably holding the electrode plate 36,the electrode plate 36 being made of a semiconductor material, e.g., Si,SiC or the like, the electrode support 38 being made of a conductivematerial, e.g., aluminum whose surface is alumite-treated. The upperelectrode 34 is attached in an electrically floating state to thechamber 10 via a ring-shaped insulator 35. A plasma generation space ora processing space PS is defined by the upper electrode 34, thesusceptor 16 and the sidewall of the chamber 10. The ring-shapedinsulator 35, which is made of, e.g., alumina (Al₂O₃), is attached sothat a gap between an outer peripheral surface of the upper electrode 34and the sidewall of the chamber 10 can be airtightly sealed. Thering-shaped insulator 35 physically holds the upper electrode 34 andelectrically forms a part of capacitance between the upper electrode 34and the chamber 10.

The electrode support 38 has therein a gas buffer space 40 and also hason its bottom surface a plurality of gas ventholes 38 a extending fromthe gas buffer space 40 to communicate with the gas injection openings36 a of the electrode plate 36. The gas buffer space 40 is connectedwith a processing gas supply source 44 via a gas supply line 42, and amass flow controller MFC 46 and an opening/closing valve 48 are providedin the gas supply line 42. When a specific processing gas is introducedfrom the processing gas supply source 44 into the gas buffer space 40,the processing gas is injected into the processing space PS toward thesemiconductor wafer W on the susceptor 16 in a shower shape from the gasinjection openings 36 a of the electrode plate 36. So, the upperelectrode 34 also serves as a shower head for supplying a processing gasinto the processing space PS.

Further, the electrode support 38 has therein a passageway (not shown)through which a coolant, e.g., cooling water, flows, so that atemperature of the entire upper electrode 34, particularly the electrodeplate 36, can be controlled to a specific level with the coolantsupplied from an external chiller unit. In order to further stabilizethe temperature control of the upper electrode 34, a heater (not shown)including, e.g., a resistance heating element may be attached to aninside or a top surface of the electrode support 39.

A hollow space or gap 50 is provided between the top surface of theupper electrode 34 and the ceiling of the chamber 10. Further, athrough-hole 52 is formed in a central portion of the top surface of thechamber 10, and a rod-shaped inductor 54 is vertically extended in thegap 50 and the through-hole 52. The rod-shaped inductor 54 has a lowerend directly connected with the central portion of the top surface ofthe upper electrode 34 and an upper end connected with a groundpotential (generally, the chamber 10) via a conducting wire.Alternatively, the upper end of the rod-shaped inductor 54 may bedirectly connected to the ceiling of the upper electrode 34.

An annular space defined by the susceptor 16, the susceptor support 14and the sidewall of the chamber 10 serves as a gas exhaust space. A gasexhaust port 58 of the chamber 10 is provided at a bottom of the gasexhaust space. A gas exhaust unit 62 is connected with the gas exhaustport 58 via a gas exhaust line 60. The gas exhaust unit 62 has a vacuumpump such as a turbo molecular pump or the like, so that the inside ofthe chamber 10, especially the processing space PS, can be depressurizedto a required vacuum level. Moreover, attached to the sidewall of thechamber 10 is a gate valve 66 for opening and closing aloading/unloading port 64 for the semiconductor wafer W.

In the plasma etching apparatus, in order to perform an etching process,the gate valve 66 is opened and a semiconductor wafer W to be processedis loaded into the chamber 10 to be mounted on the electrostatic chuck18. Then, a specific processing gas, i.e., an etching gas (generally, agaseous mixture) is supplied into the chamber 10 from the processing gassupply source 44 at a specified flow rate and flow rate ratio, while thechamber 10 is evacuated by the gas exhaust unit 62 such that theinternal pressure of the chamber 10 is maintained at a specific vacuumlevel. Further, a first radio frequency power (about 2 MHz) and a secondradio frequency power (about 40 MHz) are concurrently applied to thesusceptor 16 from the first and the second radio frequency power supply30, 70, respectively. Further, a DC voltage is applied to the electrode20 of the electrostatic chuck 18 from the DC power supply 46, wherebythe semiconductor wafer W is firmly fixed on the electrostatic chuck 18.The etching gas injected from the upper electrode 34 as the shower headis converted into a plasma by a radio frequency discharge in the plasmaspace PS, and films formed on the main surface of the semiconductorwafer W are etched by radicals or ions present in the plasma.

In such a capacitively coupled plasma etching apparatus, by applying tothe susceptor (lower electrode) 16 a first radio frequency power of arelatively radio frequency, e.g., 40 MHz, suitable for plasmageneration, a high-density plasma in a desirable dissociated state canbe generated even at a low pressure. Also, by applying to the susceptor16 a second radio frequency power of a relatively low frequency, e.g., 2MHz, suitable for ion attraction, it is possible to perform ananisotropic etching having high selectivity to the semiconductor wafer Won the electrostatic chuck 18. Further, it is also possible to remove adeposited film or an oxide film on the upper electrode 34 (electrodesurface cleaning) by the ions incident thereon or the sputtering.

Hereinafter, features of the plasma etching apparatus in accordance withthe first embodiment of the present invention will be described withreference to FIGS. 2 to 4. For convenience, the second radio frequencypower 70 that is substantially not related to the plasma generation andthe control of a plasma spatial distribution is omitted in FIGS. 2 and3.

As described above, in the plasma etching apparatus, the upper electrode34 is attached to the chamber 10 via the ring-shaped insulator 35 andthe rod-shaped inductor 54 is connected between the upper electrode 34and the ground potential. In other words, if the inductor 54 isdetached, the upper electrode 34 is installed inside the processingchamber 10 in a DC-floating state.

First of all, as for a comparative example, there will be described acase where the upper electrode 34 is directly attached to the chamber 10to be DC-connected with the ground potential, for example. In this case,as shown in FIG. 2, when the first radio frequency power from the radiofrequency power supply 30 is applied to the susceptor 16, a plasma ofthe processing gas is generated in the processing space PS by a radiofrequency discharge between the susceptor 16 and the upper electrode 34and that between the susceptor 16 and the sidewall of the chamber 10.The plasma thus generated is diffused in all directions, especially inupward and radially outward directions. Electron current in the plasmaflows toward the ground via the upper electrode 34, the sidewall of thechamber 10 or the like. In the susceptor 16, as the frequency of thefirst radio frequency power increases, a radio frequency current islikely to be gathered at the central portion of the susceptor due toskin effect and the susceptor 16 is closer to the upper electrode 34than the sidewall of the chamber 10, the upper electrode 34 and thesidewall of the chamber 10 having a same potential (ground potential).Accordingly, a larger amount of radio frequency power is discharged fromthe central portion of the electrode toward the processing space PS.Thus, most of the plasma electron current flows in the upper electrode34, especially in the central portion thereof, while a considerablysmall part of the plasma electron current flows in the sidewall of thechamber 10. As a result, the plasma density spatial distribution in thecentral portion of the electrode is highest and significantly differentfrom that in the edge portion of the electrode.

In contrast, in the embodiment of the present invention in which theupper electrode 34 is attached to the chamber 10 in a DC-floating stateand connected with the ground potential via the rod-shaped inductor 54,an equivalent circuit for a radio frequency transmission line from aboundary surface between the processing space PS and the upper electrode34 to the ground potential via the upper electrode 34 is represented bya circuit including a coil L₅₄ arranged parallel to capacitors C₃₅ andC₅₀ as shown in FIG. 3. The coil L₅₄ is an inductance of the rod-shapedinductor 5 and 4 and specifically, the coil L₅₄ is connected in serieswith a resistance (not illustrated) of the rod-shaped inductor 54. Thecapacitor C₃₅ is a capacitance between the upper electrode 34 and thesidewall of the chamber 10 and mainly formed by the ring-shapedinsulator 35. The capacitor C₅₀ is a capacitance between the upperelectrode 34 and the ceiling of the chamber 10 and mainly formed by airin the gap 50.

In this case as well, as similarly to the case shown in FIG. 2, when thefirst radio frequency power from the radio frequency power supply 30 isapplied to the susceptor 16, the plasma of the processing gas isgenerated in the processing space PS by a radio frequency dischargebetween the susceptor 16 and the upper electrode 34 and that between thesusceptor 16 and the sidewall of the chamber 10. The plasma thusgenerated is diffused in upward and radially outward directions, and anelectron current in the plasma flows toward the ground via the upperelectrode 34, the sidewall of the chamber 10 or the like. In thesusceptor 16, a radio frequency current is likely to be gathered at thecentral portion of the susceptor. Also, the susceptor 16 is locatedcloser to the upper electrode 34 than the sidewall of the chamber 10.However, a parallel LC circuit 80 including the coil L₅₄ and thecapacitors C₃₅ and C₅₀ is provided between the upper electrode 34 andthe ground potential. Therefore, when the parallel LC circuit 80provides a high impedance Z against the first radio frequency power, theradio frequency current hardly flows in the upper electrode 34 disposeddirectly above the susceptor 16 even though it is gathered at thecentral portion of the susceptor 16. Accordingly, a relatively increasedpart of the plasma electron current flows in the sidewall of the chamber10, which makes the plasma density distribution widen radially.Theoretically, depending on the impedance Z of the parallel LC circuit80, it is possible to control a ratio of the electron current flowingbetween the susceptor 16 and the upper electrode 34 and that flowingbetween the susceptor 16 and the sidewall of the chamber 10 and furtherto control the plasma density spatial distribution characteristics to beuniform in a diametric direction.

FIG. 4 describes an example of frequency-impedance characteristics for aradio frequency transmission line from the boundary surface between theprocessing space PS and the upper electrode 34 to the ground potentialvia the upper electrode in the plasma etching apparatus. In FIG. 4, animpedance X_(L) that gradually increases with respect to the frequencyis an organic reactance |jωL₅₄| of the coil L₅₄, and an impedance X_(C)that gradually decreases with respect to the frequency is a capacitivereactance |1/jω(C₃₅+C₅₀)| of the capacitors C₃₅ and C₅₀. Theoretically,the parallel LC circuit 80 causes a parallel resonance or anantiresonance at a frequency where the organic reactance X_(L) becomesequal (absolute value) to the capacitive reactance X_(C). Further, asshown in FIG. 4, an impedance Z of the parallel LC circuit 80 has amaximum peak value at the antiresonance frequency f₀. It is preferablethat the antiresonance frequency f₀ appears within a range including thefrequency of the first radio frequency power (preferably, from 5 MHz to200 MHz).

Accordingly, as illustrated in FIG. 4, by selecting or setting avariable or selectable parameter, i.e., an inductance of the inductor 54such that the antiresonance frequency f₀ appears near (preferably, at)the frequency (40 MHz) of the first radio frequency power, a high valueZ₄₀ can be selected as the impedance Z of the parallel LC circuit 80 forthe first radio frequency.

Further, as shown in FIG. 4, it is important that an impedance Z₈₀ ofthe parallel LC circuit 80 for the second radio frequency can be set tobe a value Z₂ significantly smaller than the value Z₄₀ for the firstradio frequency by setting the antiresonance frequency f₀ within therange from 5 MHz to 200 MHz. In other words, the upper electrode 34 canbe grounded at a low impedance for the second radio frequency. As aconsequence, the ions in the plasma which vibrate due to the secondradio frequency are incident on the electrode plate 36 of the upperelectrode 34 with a strong impact, thereby sputtering (removing) adeposited film or an oxide film attached on the surface of the electrodeplate 36.

FIGS. 5A and 5B illustrate, as a test example, in-surface distributioncharacteristics of etching rates of an oxide film SiO₂ and a photoresistPR by using the plasma etching apparatus of the first embodiment,respectively. In this test example, an inductance of the inductor 54 isset to be about 400 nH and a combined capacitance of the capacitors C₃₅and C₅₀ is set to be about 250 pF (low capacitance). Meanwhile, FIGS.6A, 6B and 7A, 7B present comparative examples. Referring to FIGS. 6Aand 6B, there are illustrated, as a first comparative example, spatialdistribution characteristics of the etching rates of the oxide film andthe photoresist, respectively. In the first comparative example, theinductor 54 is omitted and a combined capacitance of the capacitors C₃₅and C₅₀ is set to be about 20000 pH (high capacitance). Further,referring to FIGS. 7A and 7B, there are illustrated, as a secondcomparative example, spatial distribution characteristics of the etchingrates of the oxide film and the PR, respectively. In the secondcomparative example, the inductor 54 is omitted and a combinedcapacitance of the capacitors C₃₅ and C₅₀ is set to be about 250 pH (lowcapacitance). The test example and the comparative examples have thefollowing common etching conditions.

Wafer diameter: 300 mm

Flow rates of processing gases:C₄F₆/C₄F₈/Ar/O₂=40/20/500/60 sccm

Pressure in chamber: 30 mTorr

Radio frequency power: 40 MHz/2 MHz=2500/3200 W

Temperature of upper electrode: 60° C.

As can be seen from FIGS. 6A and 6B, in the first comparative examplewhere the inductor 54 is omitted and a ground capacitance of the upperelectrode 34 is set to be a high capacitance of about 20000 pF, theetching rates of the oxide film and the PR are relatively uniform in acentral portion of the wafer. However, the etching rates thereofabruptly decrease near an edge portion of the wafer (R=±120 mm), whichresults in poor in-surface uniformity of ±4.1% and ±19.1%.

Meanwhile, as shown in FIGS. 7A and 7B, the second comparative examplewhere the inductor 54 is omitted and a ground capacitance of the upperelectrode 34 is set to be a low capacitance of about 250 pF havesignificantly improved processing uniformity compared with the firstcomparative example. Specifically, the etching rate of the oxide film inthe central portion of the wafer is substantially same as that of thefirst comparative example, and the etching rate of the oxide film in theedge portion of the wafer increases compared with that of the firstcomparative example, which leads to improved in-surface uniformity of±2.4%. Moreover, the etching rate of the photoresist increases comparedwith that of the first comparative example and becomes uniform in eachportion of the wafer, which results in improved in-surface uniformity of±4.4%.

On the other hand, the test example has further improved processinguniformity compared with the second comparative example, as can be seenfrom FIGS. 5A and 5B. Specifically, the etching rate of the oxide filmincreases in each portion of the wafer, especially in the edge portion,compared with that of the second comparative example, which results insignificantly improved in-surface uniformity of ±1.2%. Further, theetching rate of the photoresist is substantially uniform in each portionof the wafer, which leads to improved in-surface uniformity of ±2.5%.

In general, the etching rate distribution of the oxide film reflects anelectron density distribution in plasma, i.e., a plasma densitydistribution. Further, the etching rate distribution of the photoresistis affected by a dissociation of an initial gas by the plasma and thusmore strongly depends on the plasma density distribution. Therefore, ascan be seen from the test result of FIGS. 5A and 5B, in accordance withthe test example, the uniformity of the plasma density distribution issignificantly improved by suppressing a concentration of the plasmagenerated in the processing space PS on the central portion of theelectrode and broadening the plasma radially outwardly.

As described above, the plasma density distribution can be considerablyimproved in the second comparative example compared with the firstcomparative example. However, in the second comparative example in whichthe inductor 54 is not provided, the low-capacitance (250 pF) capacitorsC₃₅ and C₅₀ forming the ground circuit of the upper electrode 34 providea considerably great impedance to the second radio frequency (2 MHz) aswell as the first radio frequency (40 MHz). More specifically, referringto FIG. 4 illustrating the frequency characteristics of the capacitivereactance X_(C), the impedance at the first radio frequency (40 MHz) ishigher than that at the second radio frequency (2 MHz). When theimpedance of the ground circuit of the upper electrode 34 is high forthe second radio frequency, the impact of ions incident on the upperelectrode 34 due to the second radio frequency becomes weak, therebydeteriorating the sputtering effect.

To that end, in the test example, the inductor 54 is provided, so thatan impedance of the parallel LC circuit 80 can be set to be high for thefirst radio frequency (40 MHz) and considerably low for the second radiofrequency (2 MHz). Accordingly, the uniformity of the plasma densitydistribution can be significantly improved. Also, it is possible tomaintain the impact intensity of ions incident on the upper electrode 34and further the sputtering effect (electrode surface cleaning effects)sufficiently high.

As a result of measuring deposition rates of deposited films on asurface of the upper electrode 34 by using as an etching gas C₄F₈ gasgenerating a large amount of polymer in the test example and the secondcomparative example, the deposition rates of 80 nm/5 min and −100 nm/5min were obtained in the test example and the second comparativeexample, respectively. In this measurement, the main etching conditionswere as follows:

Flow rates of processing gases: C₄F₆/Ar=5/1000 sccm

Pressure in chamber: 40 mTorr

Radio frequency power: 40 MHz/2 MHz=2000/400 W

Temperature: upper electrode/chamber sidewall/lowerelectrode=150/150/40° C.

Etching time: 5 min

Consequently, it has been found that the deposited film is accumulatedon the surface of the upper electrode 34 in the second comparativeexample, whereas it is efficiently removed therefrom in the etching modein the test example.

FIG. 8 illustrates a configuration of a plasma etching apparatus inaccordance with a second embodiment of the present invention. The upperend of the inductor 54 is electrically connected with a variable DCpower supply 84 via a DC filter unit 82 in the second embodiment, whileit is grounded via the conducting wire 56 in the first embodiment. Theconfigurations and functions of the other components of the secondembodiment are same as those of the first embodiment.

FIG. 9 shows an exemplary circuit configuration in the DC filter unit82. In the DC filter unit 82 of this embodiment, the inductor 54 isconnected in series with two coils 86 and 88 in a DC transmission linefrom the variable DC power supply 84 to the upper electrode 34. Further,capacitors 90 and 92 are respectively connected between a node N₁ and aground potential and between a node N₂ and the ground potential, whereinthe node N₁ is provided between the coils 86 and 88 and the node N₂ isprovided between the coil 88 and the variable DC power supply 84. Aserial-parallel LC circuit 94 is formed by the coils 86 and 88 and thecapacitors 90 and 92.

Moreover, the DC filter unit 82 may have therein a cooling (blowing)device such as a fan so as to maintain the temperatures of electricalcomponents or devices in the DC filter unit 82 at appropriate levels.Although the DC filter unit 82 can be installed at any location betweenthe inductor 54 and the variable DC power supply 84, it is preferablethat the DC filter unit 82 is mounted on a ceiling (top surface) of thechamber 10.

A DC voltage outputted from the variable DC power supply 84 is appliedto the upper electrode 34 via the coils 86 and 88 of the serial-parallelLC circuit 94 and the inductor 54. Meanwhile, when the first and thesecond radio frequency power applied from the respective radio frequencypower supplies 30 and 70 to the susceptor 16 are introduced to the upperelectrode 34 via the processing space PS, they flow to the ground viathe inductor 54 and the serial-parallel LC circuit 94 in the DC filterunit 82 while hardly flowing to the variable DC power supply 84.

The variable DC power supply 84 is configured to output a DC voltagehaving a polarity and a voltage level selected depending on processingtypes or conditions. It has been known that, by applying a proper DCvoltage to the upper electrode 34, at least one of following effects canbe obtained: (1) sputtering effect (deposit removal effect) on the upperelectrode 34 is enhanced by increasing an absolute value of a self-biasvoltage of the upper electrode 34; (2) the generation amount of plasmais reduced by enlarging a plasma sheath with respect to the upperelectrode 34; (3) electrons generated near the upper electrode 34 areirradiated onto a target substrate (semiconductor wafer W); (4) a plasmapotential can be controlled; (5) electron density (plasma density) isincreased; and (6) the plasma density in the central portion isincreased. For a case where it is not required to apply a DC voltage tobe applied to the upper electrode 34, it is preferable to provide anon/off switch 96 including, e.g., a relay switch between the variable DCpower supply 84 and the serial-parallel LC circuit 94.

In the second embodiment, the serial-parallel LC circuit 94 in the DCfilter unit 82 allows the DC voltage from the variable DC power supply84 to flow therethrough to the upper electrode 34 and generates a serialresonance at a low frequency range (preferably, from 100 kHz to 15 MHz)and a parallel resonance at a radio frequency range (preferably, from 5MHz to 200 MHz) with respect to the radio frequency from the upperelectrode 34. By utilizing such frequency-impedance characteristics ofthe serial-parallel LC circuit 94, it is possible to further improve theindividual functions of the first and the second radio frequency in thedual frequency application type wherein two radio frequency powers areapplied to the lower electrode.

FIG. 10 depicts, as an example, frequency-impedance characteristics Z₉₄of the serial-parallel LC circuit 94 alone in this embodiment andfrequency-impedance characteristics Z_(A) in a radio frequencytransmission line from a boundary surface between the processing spacePS and the upper electrode 34 to the ground potential via the upperelectrode 34.

As shown in FIG. 10, in this example, a resonance frequency and anantiresonance frequency of the serial-parallel LC circuit 94 are set tobe about 2 MHZ and about 45 MHZ, respectively. In thefrequency-impedance characteristics Z₉₄, a considerably high impedanceof about 1000Ω corresponds to the first radio frequency (40 MHz),whereas an extremely low impedance of about 1Ω corresponds to the secondradio frequency (2 MHz). In the frequency-impedance characteristicsZ_(A) of the entire ground circuit around the upper electrode 34 whereinthe inductor 54, the capacitors C₃₅, C₅₀ and the like are added to theserial-parallel LC circuit 94, the antiresonance frequency is shifted tothe low frequency range up to about 10 MHz, whereas the resonancefrequency is maintained near about 2 MHz. Further, while the impedancecorresponding to the first radio frequency (40 MHZ) is considerablyreduced to about 20Ω, the impedance corresponding to the second radiofrequency (2 MHZ) is slightly reduced to about 0.7Ω, and the differencetherebetween is still maintained more than 20 times.

A noticeable point in FIG. 10 is that the impedance corresponding to thesecond radio frequency (2 MHZ) in the frequency-impedancecharacteristics Z_(A) of the entire ground circuit around the upperelectrode 34 can be lowered to 1Ω or less by utilizing a resonancephenomenon of the serial-parallel LC circuit 94. As a consequence, theupper electrode 34 is seemingly short-circuited to the ground potential(imaginary short-circuit state) in view of the second radio frequency (2MHz), which enhances the impact intensity of ions incident on the upperelectrode 34 due to the vibrations of the second radio frequency andfurther the sputtering effect (deposit removal effect).

The frequency-impedance characteristics Z₉₄ and Z_(A) shown in FIG. 10are provided for illustrative purpose only and can be modified oradjusted by varying inductance values of the coils 86 and 88 andcapacitance values of the capacitors 90 and 92 in the serial-parallel LCcircuit 94.

Further, the circuit configuration shown in FIG. 9 is provided forillustrative purpose only, and a modification can be made in or aroundthe DC filter unit 82. For example, in the serial-parallel LC circuit94, the number of coils and capacitors may be changed, the circuitnetwork may be formed in T type, π type or the like without beinglimited to that shown in FIG. 9. Besides, a circuit element having adifferent function, e.g., a noise removing coil (not shown) or the like,may be inserted between the serial-parallel LC circuit 94 and thevariable DC power supply 84.

Moreover, a variable impedance element may be provided in the DC filterunit 82. For example, as shown in FIG. 11, the coil 86 and thecapacitors 90 may be made to serve as a variable reactor and a variablecapacitor, respectively.

Instead of the serial-parallel LC circuit 94, the upper electrode 34 maybe grounded via a serial LC circuit 100 including the inductor 54 and acapacitor 98, as shown in FIG. 12. In this case, as an entire groundcircuit around the upper electrode 34, i.e., as an equivalent circuit ina radio frequency transmission line from the boundary surface betweenthe processing space PS and the upper electrode 34 to the groundpotential via the upper electrode 34, there is formed a serial-parallelLC circuit (not shown) in which the capacitors C₃₅ and C₅₀ (see, FIG. 3)are connected with the serial LC circuit 100 in parallel. In thefrequency-impedance characteristics of the serial-parallel LC circuit,as similar to that in FIG. 10, an inductance of the inductor 54 and acapacitance of the capacitor 98 is preferred to be set such that adesired resonance frequency and a desired antiresonance frequency higherthan the resonance frequency are obtained in respective frequencyranges, and preferably such that the resonance frequency is obtainednear the frequency of the second radio frequency power.

Further, in case the variable DC power supply 84 is used, an outputterminal of the variable DC power supply 84 is preferably electricallyconnected with a node N_(a) provided between the inductor 54 and thecapacitor 98, as shown in FIG. 12. Moreover, the variable DC powersupply 84 may be omitted. In such a case, the inductor 54 and thecapacitor 98 may be exchanged with respect to the upper electrode 34. Inother words, the capacitor 98 may be connected in series between theupper electrode 34 and the inductor 54. The inductor 54 is not limitedto a rod-shaped conductor and may be formed of a coil-shaped conductoror any inductive element or member for providing a capacitive impedance.

Further, it is possible to vary an electrostatic capacitance or a groundcapacitance around the upper electrode 34 in the plasma etchingapparatus of the above embodiments. FIGS. 13 to 15 show exemplaryconfigurations of a capacitance varying unit.

Capacitance varying units 102 and 102′ shown in FIGS. 13 and 14respectively include conductive plates 104 and 104′ movable between afirst position where it contacts with or adjacent to a top surface ofthe upper electrode 34 and a second position upwardly spaced from theupper electrode 34; manipulating mechanisms 106 and 106′ for verticallymoving or displacing the conductive plates 104 and 104′; and acapacitance controller 108 for controlling a ground capacitance of theupper electrode 34 to a desired level by using the manipulatingmechanisms 106 and 106′. The manipulating mechanism 106 of FIG. 13,which is grounded directly or via the chamber, is made of a conductivematerial, a material conductive to a radio frequency, or a materialhaving a low impedance to a radio frequency. The manipulating mechanism106′ of FIG. 14 may be made of an insulating material. In suchcapacitance varying types, a ground capacitance of the upper electrode34 can be varied depending on the height positions of the conductiveplates 104 and 104′. The closer the conductive plates 104 and 104′ areto the ceiling surface of the chamber 10, the smaller the groundcapacitance of the upper electrode 34 becomes. On the contrary, thecloser the conductive plates 104 and 104′ are to the top surface of theupper electrode 34, the grater the ground capacitance of the upperelectrode 34 becomes. To be extreme, it is possible to make the groundcapacitance infinite by allowing the upper electrode 34 to be groundedvia the conductive plates 104 and 104′ contacted therewith.

A capacitance varying unit 102″ shown in FIG. 15 includes an annularliquid chamber 110 formed in the ring-shaped insulator 35 providedbetween the upper electrode 34 and the sidewall of the chamber 10. Aliquid Q having an appropriate dielectric constant (for example, anorganic solvent such as Galden or the like) can be supplied from theoutside of the chamber 10 into the liquid chamber 110 via a line 112 andremoved therefrom. By changing the kind (dielectric constant) or theamount of the liquid Q, an electrostatic capacitance of the entirering-shaped insulator 35 and further a ground capacitance of the upperelectrode 34 can be varied.

Alternatively, a variable capacitor (not shown) may be connected betweenthe upper electrode 34 and the chamber 10.

Any frequency-impedance characteristics can be realized by appropriatelycombining the variable capacitor, the capacitance varying unit 102, avariable inductance element (not shown) for varying an inductance of theinductor 54, the variable impedance element in the DC filter unit 82shown in FIG. 11 and the like. More specifically, an impedance to thefirst radio frequency for plasma generation can be adjusted by theaforementioned variable capacitor or the capacitance varying unit 102,while an impedance to the second radio frequency for ion attraction canbe adjusted by the variable impedance element in the DC filter unit 82.

As another embodiment of the present invention, a configuration shown inFIG. 16 may be employed. Specifically, the first radio frequency poweris supplied from the radio frequency power supply 30 to the susceptor 16via the matching unit 32 and the power feed rod 33 while the secondradio frequency power is supplied from the radio frequency power supply70 to the susceptor 16 via the matching unit 72 and the power feed rod74 (the type in which dual frequency powers are applied to the lowerelectrode). Further, the upper electrode is divided in a radialdirection into a disk-shaped inner upper electrode 34A and a ring-shapedouter upper electrode 122. A ring-shaped insulator 120 is insertedbetween the inner upper electrode 34A and the outer upper electrode 122and, also, a ring-shaped insulator 124 is inserted between the outerupper electrode 122 and the sidewall of the chamber 10. Such aconfiguration enables the first radio frequency power of a radiofrequency to flow mainly in a path to the sidewall (earth) of thechamber 10 via the outer upper electrode 122 and the second radiofrequency power of a low frequency to flow mainly in a path to the earthvia the inner upper electrode 34A and the power feed rod 52.

The frequencies of the first and the second radio frequency power areused as illustrative purpose only in the above embodiments, and anyfrequency can be selected depending on processes. In general, the firstradio frequency power for plasma generation has a frequency of about13.56 MHz or greater, and the second radio frequency power for ionattraction to the substrate or the upper electrode has a frequency ofabout 13.56 MHz or less.

The ground circuit around the upper electrode 34 in the aforementionedembodiments has been described for illustrative purpose only, andvarious modifications can be made to configurations and functions of thecomponents of the apparatus. Although the above embodiments have beendescribed with respect to the plasma etching apparatus and method, butthe present invention may be applied to other parallel plate type plasmaprocessing apparatus and method such as plasma chemical vapor deposition(CVD), plasma oxidation, plasma nitridation, sputtering and the like.Further, the substrate to be processed is not limited to thesemiconductor wafer, but it may be a flat panel display substrate, aphoto mask, a compact disk (CD) substrate, a printed substrate or thelike.

While the invention has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modification may be made without departing from thescope of the invention as defined in the following claims.

What is claimed is:
 1. A plasma processing apparatus comprising: anevacuable processing chamber which is grounded; a first electrodeattached to the processing chamber via an insulating material or aspace; a second electrode disposed in parallel with the first electrodespace apart therefrom in the processing chamber, the second electrodesupporting a target substrate to face the first electrode; a first radiofrequency power supply unit for applying a first radio frequency powerof a first frequency to the second electrode; a second radio frequencypower supply unit for applying a second radio frequency power of asecond frequency lower than the first frequency to the second electrode;a processing gas supply unit for supplying a processing gas to aprocessing space formed by the first and the second electrode and asidewall of the processing chamber; a DC power supply for applying a DCvoltage to the first electrode; and a filter electrically connectedbetween the first electrode and the DC power supply, the filter allowinga direct current to substantially pass therethrough and having aresonance frequency associated with the second frequency and anantiresonance frequency associated with the first frequency.
 2. Theplasma processing apparatus of claim 1, wherein the filter has pluralinductors electrically connected in series in a DC transmission linebetween the first electrode and the DC power supply; and respectivecapacitors connected between a ground potential and nodes provided inthe DC transmission line.
 3. The plasma processing apparatus of claim 1,wherein an impedance of the filter corresponding to the second frequencyis lower than that corresponding to the first frequency.
 4. The plasmaprocessing apparatus of claim 3, wherein the resonance frequency is setwithin a range from about 100 kHz to about 15 MHz and the antiresonancefrequency is set within a range from about 5 MHz to about 200 MHz. 5.The plasma processing apparatus of claim 4, wherein the resonancefrequency is substantially equal or close to the second frequency. 6.The plasma processing apparatus of claim 1, wherein frequency-impedancecharacteristics of the filter are set to obtain desired plasma densitydistribution characteristics for a plasma generated in the processingspace.
 7. The plasma processing apparatus of claim 1, wherein the firstfrequency is about 27 MHz or greater.
 8. The plasma processing apparatusof claim 7, wherein the first frequency is about 40 MHz or greater. 9.The plasma processing apparatus of claim 1, wherein the second frequencyis about 13.56 MHz or less.
 10. The plasma processing apparatus of claim1, wherein the first and the second electrode serve as an upperelectrode and a lower electrode, respectively.
 11. The plasma processingapparatus of claim 10, wherein a gas chamber into which the processinggas from the processing gas supply unit is introduced is provided aboveor at an upper portion of the first electrode, and a plurality of gasinjection openings for injecting the processing gas from the gas chamberinto the processing space are formed in the first electrode.
 12. Theplasma processing apparatus of claim 1, wherein a ring-shaped insulatoris airtightly provided between the first electrode and the sidewall ofthe processing chamber.
 13. The plasma processing apparatus of claim 1,wherein the filter is set to enhance at the second frequency an impactintensity of ions from a plasma in the processing chamber on the firstelectrode.
 14. The plasma processing apparatus of claim 1, wherein thefilter connected to the DC power supply comprises variable reactancecomponents.
 15. The plasma processing apparatus of claim 1, wherein thefilter connected to the DC power supply comprises a rf frequencytransmission line.